Method and device for testing the measuring value of at least one level sensor arranged in a fuel tank.
The invention relates to a method for checking for faults in the measured value or values of one or more filling level sensors arranged in a fuel tank of a motor vehicle. Defects in the filling level sensors can lead to an incorrect display of the contents of the fuel tank. This entails the risk of the motor vehicle becoming immobile as a result of an empty fuel tank, which is particularly dangerous if this occurs on a freeway.
When there are a plurality of filling level sensors, such as is the case for example in saddle-type fuel tank systems with a plurality of chambers of the fuel tank, the risk of an incorrect display of the contents of the fuel tank is higher the greater the number of filling level sensors.
The object of the invention is therefore a method and a device for carrying out the method of the type mentioned at the beginning by which the fault or faults of the filling level sensor or sensors can be detected.
This object is achieved according to the invention in that the measured values of a plurality of measurements are sensed and are each compared with a further physical variable for plausibility, and in that if they are not plausible a warning signal is fed to a warning device and a warning information item is triggered by the warning device.
As a result of this design, a warning information item is issued immediately after it has been determined that the values are not plausible. The acquisition of a plurality of measurements avoids the possibility of a warning being issued if just one of the plurality of measurements is not plausible but the other measurements are plausible.
The plurality of measurements preferably take place within a specific time period.
A measurement interval with the plurality of measurements can each be triggered after expiry of a specific operating time of the engine or by means of a specific operating function of the motor vehicle.
Such a specific operating function can be the switching on or the switching off of the ignition or an idling mode of the engine.
It is thus not necessary to carry out monitoring continuously but rather only on specific occasions.
In order to acquire the measured values of a plurality of measurements when there is a fuel tank having a plurality of chambers, the measured values of the filling level sensors which are arranged in the chambers are summed and the sum of measured values is compared with the further physical variable for plausibility.
One possibility for a physical variable for determining the plausibility is for the further physical variable to be the value of a quantity of fuel which is extracted from the fuel tank by a fuel pump and which, for the determination of the plausibility, yields an approximately constant value when added to the measured value or values of the filling level sensors for at least a plurality of the measurements.
In another possibility, the physical variable can be the value of the quantity of fuel which is injected into the engine of the motor vehicle by an injection system and which, for the determination of the plausibility, yields an approximately constant value when added to the measured value or values of the filling level sensors for at least a plurality of the measurements.
No further measured values are supplied and it is thus particularly easy that the further physical variable is the measured value of a measurement or the measured value of a plurality of the measurements which, for the determination of the plausibility, yield approximately constant values when they are compared with one another.
The warning information item can be a visual and/or an audible warning information item.
In order to reliably avoid displaying a larger value for the contents of a fuel tank than is actually present, the warning signal can trigger the display of an empty fuel tank on a filling level display.
However, it can also switch on a fault information display.
The second part of the object is achieved with a device for carrying out the method by virtue of the fact that a filling level sensor is arranged in a fuel tank, the measured values of which sensor can be fed to a computer unit and can be compared with one or more measured values of one or more measured values which are determined previously, the computer unit being able to generate a warning signal if the measured value deviates from the previously determined measured values.
This object is also achieved by virtue of the fact that the at least two filling level sensors are arranged in a fuel tank, the measured values of which sensors can be fed to a computer unit and can be summed by the computer unit to form a measured value sum, and can be compared with a measured value sum, of one or more previously determined measured value sums, the computer unit being able to generate a warning signal if the measured value sum deviates from the previously determined measured value sums.
The computer unit can at the same time be used for actuating a filling level display which can display a filling level corresponding to the measured value sum.
One possibility for the warning information item is that a fault information display can be actuated by the warning signal.
However, it is also possible for the filling level display to be actuated by the warning signal.
This can be done, for example, by the filling level display displaying the filling level zero or being actuated so as to flash.
A particularly advantageous application is that the fuel tank is a fuel tank which has a plurality of fuel chambers, at least one filling level sensor being arranged in each chamber.
One of the chambers can be a main chamber and the other chambers can be secondary chambers, a fuel pump by which fuel can be delivered to an internal combustion engine being arranged in the main chamber.
If pumps by which fuel can be delivered from the secondary chambers into the main chamber are arranged in the secondary chambers, a plausibility check is nevertheless possible since the measured value sum of measured values of all the filling level sensors is always formed.
One simple and cost-effective embodiment of the pumps is possible by virtue of the fact that the pumps are suction jet pumps which can be driven by a branch of the delivery current of the fuel pump.
If the fuel pump can be open-loop or closed-loop controlled by the computer unit, only corresponding programming of the computer unit but no separate electronics is required.